Safety device for blasting cables



Patented Mar. 18, 1941 UNITED STATES- SAFETY DEVICE FOR BLASTING CABLES Thomas 0. Luke and Albert Mariotti, McComas, W. Va., assignors of one-fourth to Carl Mariotti Application May 23, 1939, Serial No. 275,308

1 Claim. (Cl. 200-168) This invention relates to a safety device for use in connection with a cable used from a. battery to a detonator or blasting cap as in mines, which require that the wires of the cable be normally shunted or short-circuited.

It is especially aimed to provide a construction in which the shunting or short-circuiting iseffected within a rubber or other pliable element adapted for compression to separate the con- 10 tacts or conductors when a circuit is to pass therethrough.

It is also aimed to provide such a structure with one dimension preferably. greater than the other, so that when the device rests upon the 15 ground and is accidentally tread upon, the contacts will be brought into more effective shunting or short-circuiting engagement, rather than being opened or separated.

The more specific objects and advantages will 20 become apparent from a consideration of the description following taken in connection with the accompanying drawing illustrating an operative embodiment.

In said drawing:

Figure 1 is a view in side elevation showing our improvements applied to a cable;

Figure 2 is a view taken at a right angle to Figure 1;

Figure 3 is a plan view;

30 Figure 4 is a vertical section taken on the line 4-4 of Figure 3;

Figure 5 is a view taken through the device at a right angle to Figure 4; with one of the block sections removed;

35 Figure 6 is across sectional view taken on the plane of line 6-6 of Figure 1, and

Figure '7 is a View similar to Figure 5 but presuming flattening or compression of the blocks to separate the contacts.

Referring specifically to the drawing wherein like reference characters designate like or similar par-ts, H) represents conductors as used to provide an electric circuit from a battery (not shown) to a blasting cap or detonator as used in a mine. Normally, the wires H] for safe purposes, are required to be shunted or short-circuited by contact with each other, to prevent danger of accidental or premature blasting.

When the wires are directly joined or twisted together, they soon lose their efiec'tiveness by crystallization and the like.

According to the present invention, portions of each wire have the insulation 'll removed therefrom as at 12 and are secured within contacts a 13 generally of H-shape as best shown in Figure 6. Such contacts consist of a single strip of metal bent to form a double flange at M at opposite sides thereof, terminal flanges l5 at opposite sides therefrom, and webs It connecting the flanges i5 and M. The webs H5 may be soldered 5 together and portions I-Z soldered to the adjacent portions of the contacts to effect better connections,

Said contacts have enlargements or wings at H which are normally in engagement to shunt or short-circuit the conductors Ill.

Said contacts are suitably embedded in a manually compressible body It usually consisting of sections ll! of pliable rubber or other insulation which are cemented or joined together at a junc- 15 Tim plane 20. It will be noted that the flanges l5 occupy recesses or spaces 24 in the sections l9 while the flanges l4 occupy a central recess or spac 22 of the blocks. To insure suflicient spread of the contacts I! to prevent short-circuiting the detonator circuit the body portion [8 is provided with recessed portions 23 communieating with recess or space 22.

As stated, the circuit will normally be shunted or short-circuit-ed since the contacts are in en- 25 gagement at the flanges ll and are urged into and maintained in such engagement through the contractile action of the rubber sections l9. However, at th time an electric circuit is to be passed through the conductors 12 to fire a detonator or blasting cap, the body I8 is compressed at its greater transverse dimension as at the points and in the directions indicated by the arrows in Figure 6. Such action causes, the rubber body I3 to bulge at a right angle to the line of compression, thereby separating the contact portions I l and hence an electric circuit may readily be closed through the conductors from the battery to the detonator or blasting cap. However, upon release of the elastic body, it will assume its normal position, shown in the drawing, again shunting or short-circuiting the wires l0.

Attention is called to the fact that if the structure should rest on the ground, and be tread upon, such treading would tend to establish more firm contact between the portions I1, since the body would fall and rest on its wider rather than narrower dimension.

Various changes may be resorted to provided they fall within the spirit and scope of the invention.

We claim as our invention:

A device of the class described having a resilient body, conductor means passing through the body, said conductor means having portions normally maintained in contact by the resilience of said body to provide a. short circuit and adapted for separation through compression of the body -to enable closing of a circuit rthmough the conductor means, said conductors including contacts tacts are anchored to .the body rto move with and through the compression of the latter, said contac-ts being in a single strip and enclosing a portion of the conductors and generally being of H- shape to provide inner and outer flanges, the body 5 having a recess, the inner flanges of boih contacts being located within said recess.

THOMAS C. LUKE. ALBERT MARIOTTI. 

